If you're a civil servant in a department, you've worked there for years, you know why things are done the way they are, you know the pitfalls and the edge cases, you know the stake holders etc, etc, etc.

Some politician gets elected on a pledge to, eg, change the side of the road people drive on. Simple right? Set a date for next month as the switch over date, send a letter telling everyone, simple.

Except lane markings need changing, signs need changing, and most of those aren't directly under your control. Insurers are up in arms because all the cars are set up for driving on one side of the road. Some disability group is sueing because a proper safety study wasn't done, engineers can't guarantee that going on the off ramps and off the on ramps is safe, because they were never designed for that and theres 10000 other assumptions that were made on the basis of driving on one side of the road that are now invalidated, and its your job to point that out to your new boss.